1. Field of the Invention
The present invention relates to a calibration of a weight measuring apparatus, and more particularly to a weight applying unit for performing a calibration on a weight measuring apparatus comprising a plurality of load sensors and a weight applying method of performing the same.
2. Description of the Background Art
In a weight measuring apparatus, using a load sensor, which is typified by a scale or the like, a calibration is performed on a load sensor-integrated weight measuring apparatus as a finished product, in order to improve an accuracy of measurement results. As a calibration method used for a weight measuring apparatus using a single load sensor, for example, a specific load of a weight is placed on a load platform at a center position thereof, and a calibration is performed based on a detected output of the load sensor. Also, there may be another weight measuring apparatus in which a single load platform is supported by a plurality of load sensors, and detected outputs of the plurality of respective load sensors are added to each other so as to obtain a weight value. Similarly to the weight measuring apparatus using the single load sensor, as a calibration method used for said another weight measuring apparatus comprising the plurality of load sensors, a specific load of a weight is placed on the load platform at a center position thereof, and a calibration is performed based on a total value of the detected outputs of the respective load sensors. Furthermore, as another calibration method, specific loads of weights are respectively placed on a load platform at predetermined positions such as four corners of the load platform, thereby performing a calibration based on detected outputs of the respective load sensors (Japanese Laid-Open Patent Publication No. 3-25325, for example).
In recent years, in the field of home fitness apparatuses or video games, when using the weight measuring apparatus comprising the plurality of load sensors, for example, it is requested that the weight measuring apparatus not only output the weight of a to-be-measured object placed on a load platform, but also recognize a balance state of the to-be-measured object such as the postural balance of a person on the load platform. In order to recognize the balance state of the to-be-measured object (e.g., a state where a human stands on his or her right foot and a greater amount of load is applied to a right side of the load platform), loads applied to the plurality of load sensors must be individually obtained. Further, in order to improve an accuracy of measurement results detected by the respective load sensors, a calibration must be performed on each of the load sensors, instead of performing the calibration based on the total value of the detected outputs of the respective load sensors.
In such a weight measuring apparatus integrated with the plurality of load sensors, as a method of performing a calibration on each of the load sensors, there may be a method in which the specific loads of the weights are placed on a load platform in respective four corners thereof, thereby performing the calibration on each of the load sensors based on an output of each of the load sensors (not based on the total value of the outputs of the respective load sensors), as disclosed in Japanese Laid-Open Patent Publication No. 3-25325.
However, in the aforementioned calibration method in which the weights are respectively placed in the four corners of the load platform, the weights are placed on the load platform, and therefore a load of each of the weights, which naturally should be applied in a perpendicular direction, is to be dispersed in other directions. For example, in the case of a weight measuring apparatus in which a load platform is supported by two load sensors 91 and 92 as shown in FIG. 17, it is assumed that a weight of 50 kg is placed on the load platform at a right side thereof. In this case, a value of 40 kg is detected in the load sensor 92 located under the weight, while a value of 10 kg is detected in the other load sensor 31, for example. That is, a load of 50 kg is distributed between the two load sensors. Furthermore, the value of 40 kg or 10 kg is used as an example in FIG. 17 in order to facilitate the description. In practice, however, it is difficult to accurately recognize how and in which direction the load of 50 kg is dispersed. Therefore, in such a calibration method, when a calibration is performed on each of the load sensors, it is extremely difficult to perform a proper calibration.